Human skin is the largest organ. Aside from the function of regulating skin temperature, the skin's most important function is to serve as an effective barrier against insult of the body by foreign agents, such as toxic substances, microorganisms, and due to mechanical injury. Human skin comprises several layers: the outermost is the stratum corneum, which comprises dead skin cells and makes up a substantial portion of the first protective barrier of the body. Most skin comprises a stratum corneum which is 15–20 layers of dead cells thick (about 10–20 microns in thickness). However, some “durable” skin layers, such as heels or calluses, can comprise a stratum corneum which is from 100–150 microns thick. On average, the skin naturally sheds at least one skin layer each day, and the first one to four layers of skin may be removed without affecting the protective nature of skin or the health thereof In fact, removing up to four (4) layers of the stratum corneum may provide a skin surface area onto which make-up may be more uniformly applied and once applied has a more aesthetically pleasing appearance.
Penetration of the outer layers of skin to deliver a pharmaceutical composition is a widely held practice. Typically injections of pharmaceuticals are affected by subcutaneous delivery, intramuscular delivery, as well as intravenous delivery. Less invasive procedures have now been developed and are widely utilized. Among these “topical” applications are patches, which are used to provide slow release of a composition, such as air and motion sickness compositions, or cigarette smoking abatement compositions. However, these patch delivery systems rely on formulations that can carry the active ingredients across the skin barrier into the blood stream. Therefore, formulation and dosing limitations may provide an encumbrance to delivery of a medication or skin benefit composition via patch.
There is, therefore, a long felt need for an article of manufacture that can be used to deliver a composition cutaneously (or subcutaneously) to skin. Specifically, there is also a need for article that is capable of lancing the surface of skin or is capable of penetrating the surface of skin to a depth where a composition can be efficaciously applied.
One solution to the above-noted long felt need is a “patch” that contains a plurality of microneedles, in which each individual microneedle is designed to puncture the skin up to a predetermined distance, which typically is greater than the nominal thickness of the stratum corneum layer of skin. Using such microneedle patches provides a great benefit in that the barrier properties of the skin can be largely overcome, while at the same time the microneedles can be painless and bloodless if they are made to not penetrate through the epidermis.
One problem with microneedles is that, first they require a direct pushing motion against the skin, which may or may not be of sufficient force to penetrate completely through the stratum corneum and, second even when they do penetrate the stratum corneum, their efficiency of compelling a fluid (such as a liquid drug or other active) though their relatively tiny openings is not great (these microneedles are usually quite small in diameter). It would be an improvement to provide a microstructure (e.g., in the form of a hand-held patch) that can provide a greater efficiency of flow for some type of fluidic compound through the stratum corneum, and to make it possible for the microstructure to penetrate the outer skin layers (e.g., the stratum corneum) by a sliding or rubbing motion that is essentially parallel to the skin surface, rather than perpendicular to the skin surface. The sliding/rubbing motion allows each microelement protruding from the substrate (or base) of the microstructure to make multiple slits or cuts in the outer layers of the skin, which increases the permeability of the skin (i.e., it reduces the skin's barrier properties) at that local area.